1. Field of the Invention
The present invention relates to an auxiliary module, and more particularly to an electrical auxiliary module for a vehicle steering system to improve mechanical efficiency of the steering system.
2. Description of Related Art
An auxiliary device is mounted on a vehicle steering system to provide an auxiliary torque/force for the steering system. However, the conventional auxiliary device is a specific design based on different types or structures of vehicles, so to design and to manufacture a conventional auxiliary device are sophisticated and time-consuming.
With reference to FIG. 9, a conventional pinion type of auxiliary device (70) for a vehicle steering system comprises a gear assembly (72) having a worm gear to transmit power provided by a motor to the steering system. However, the conventional auxiliary device (70) has the following drawbacks.                1. Long design term. The conventional auxiliary device (70) has to be designed and manufactured based on different types and structures of vehicles. The design term for the conventional auxiliary device (70) is long, and molds for manufacturing components of the specific conventional auxiliary device (70) have to be designed accordingly.        2. Low mechanical efficiency. The gear assembly (72) in the conventional auxiliary device (70) comprises a worm rod and a worm gear, but the mechanical efficiency of the conventional gear assembly (72) is low and about 85%. Therefore, the conventional auxiliary device (70) has high power/oil consumption and cost.        3. Troublesome repairing process. To repair or replace damaged component of the conventional auxiliary device (70), the auxiliary device (70) even the whole steering system has to be detached or disassembled. After the repairing or replacing process, the wheels of the vehicle should also be aligned again and this is inconvenient and time-consuming.        
In addition, U.S. Pat. No. 7,412,906 disclosed a power steering system having a planetary gear transmission and an output drive gear that engages a driven gear mounted around an output shaft. However, the planetary gear transmission of the '906 Patent is far away from the output drive gear, such that the volume of the power steering system of the '906 Patent is too large to fit with a small vehicle. The power steering system disclosed by the '906 Patent is not versatile and convenient in use.
To overcome the shortcomings, the present invention tends to provide an electrical auxiliary module to mitigate or obviate the aforementioned problems.